idle surging--need help!!

[dusted800]

Have a 91 C1500 with 305, 5 speed. Truck starts good, comes up on a high idle for a few minutes and then idle settles down,runs for a few mor minutes and then idlegoes down hill and computer catches it and speeds it up, and then after 30 seconds it starts going down again and it surges back up again. and this continues as long as it idles. No codes are set check engine light doesn't come on. I have been told to check distributor,throttle position sensor,map sensor.I am not up on much of this computer controlled stuff. Anyone give me some suggestions regarding this old girl. thanx. wnk.

[mcreyaufmiller]

I would check your TPS. The computer does not know where the throttle is and lets the idle fall, and then kicks it back up when it gets too low. Put a computer on it, even though your engine light is not on, it may be blown. You can check when you start your truck, it should come on for a sec then shut off.

 

Mike

[Mike G]

I would check your TPS.

Mike

 

 

Just in case for WNK, TPS = Throttle Position Sensor. This should be located on the passenger side of your "carb", a little black unit that attaches to the butterfly's shaft with a three wire plug in it. Costs about $40 (put then most of the sensors do) and takes all of 60 seconds to replace.

 

--Mike (G)